1. Field of the Invention
The present invention relates to an information recording device which magnetically records information which consists of a plurality of bits by a PPM recording method.
2. Related Background Art
The PPM (pulse position modulation) recording method is a per se known method of magnetically recording data upon a magnetic recording medium.
FIG. 9 is a waveform diagram illustrating this PPM recording method.
With the PPM recording method, the period of the signal is always kept fixed, and the signal levels "0" and "1" are coded by the position of the trailing edge of the signal waveform. In concrete terms, if the trailing edge of the signal waveform occurs between the start point of the period of the signal and its midpoint this is taken as encoding a "0", while if the trailing edge of the signal waveform occurs between the midpoint of the period of the signal and its end point this is taken as encoding a "1". For example, referring to FIG. 9, when the trailing edge of the signal waveform occurs at a position approximately one quarter period from the head of the signal period this is taken as encoding a "0" (in this case, called a PPM signal of 25% bit location), while when the trailing edge of the signal waveform occurs at a position approximately three quarters period from the head of the signal period this is taken as encoding a "1" (in this case, called a PPM signal of 75% bit location ).
The above method enables data to be transmitted correctly even if the trailing edge position in the signal period is somewhat shifted due to a delay over the data line or other cause. When data of "0" is to be transmitted in FIG. 9, it is recognized as data of "0" so long as the signal waveform drops before its half period, even if the data that should drop at one quarter period from the head of the signal period is lagged to actually drop behind the quarter period due to a delay over the data line or other cause. As a result, an error in transmission of data is less likely to occur.
Meanwhile, there are known cameras of the type magnetically recording photographic information, such as the date and exposure data, on a film, and there is also a possibility of taking advantage of the above described PPM recording method for such magnetic recording.
This type of camera generally performs the magnetic recording utilizing movement of the film when it is being wound on each after taking a photography. However, because when the film is being wound on there are fixed limits to the speed of feeding of the film and to the amount by which the film is wound on, the amount of data which can be recorded magnetically upon the film at this time is restricted to being within a fixed scope. Accordingly, if more information is required to be thus magnetically recorded, it is necessary to provide a plurality of magnetic recording tracks on the film.
However, in order to perform magnetic recording of a plurality of magnetic tracks during the short time period while the film is being wound on from one frame to another, several streams of serial data must be supplied separately to a plurality of magnetic heads at the same time, and these magnetic heads must be separately driven. For this reason, it is necessary to provide a special type of CPU which is capable of outputting several streams of serial data at the same time, which is expensive and bulky. Further it is necessary to provide a plurality of serial data lines for these serial data streams between such a CPU and a PPM conversion circuit section which converts the serial data streams into PPM format, and it causes the problem that the reliability of the device deteriorates due to this increase in the number of signal lines.